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Overview

The Cart library (system/library/cart/cart.php) manages shopping cart operations including adding products, calculating totals, and handling product options.

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Cart Class

From system/library/cart/cart.php:8: 
namespace Opencart\System\Library\Cart;

class Cart {
    private object $db;
    private object $config;
    private object $customer;
    private object $session;
    private object $tax;
    private object $weight;
    private array $data = [];
    
    public function __construct(\Opencart\System\Engine\Registry $registry) {
        $this->db = $registry->get('db');
        $this->config = $registry->get('config');
        $this->customer = $registry->get('customer');
        $this->session = $registry->get('session');
        $this->tax = $registry->get('tax');
        $this->weight = $registry->get('weight');
    }
}

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Core Methods

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Adding Products

From system/library/cart/cart.php:321: 
/**
 * Add product to cart
 *
 * @param int   $product_id
 * @param int   $quantity
 * @param array $option
 * @param int   $subscription_plan_id
 * @param array $override
 */
public function add(int $product_id, int $quantity = 1, array $option = [], int $subscription_plan_id = 0, array $override = []): void {
    $this->db->query("
        INSERT INTO `" . DB_PREFIX . "cart` 
        SET `store_id` = '" . (int)$this->config->get('config_store_id') . "',
            `customer_id` = '" . (int)$this->customer->getId() . "',
            `session_id` = '" . $this->db->escape($this->session->getId()) . "',
            `product_id` = '" . (int)$product_id . "',
            `subscription_plan_id` = '" . (int)$subscription_plan_id . "',
            `option` = '" . $this->db->escape(json_encode($option)) . "',
            `quantity` = '" . (int)$quantity . "',
            `override` = '" . $this->db->escape(json_encode($override)) . "',
            `date_added` = NOW()
    ");
    
    $this->data = [];
}

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Updating Quantity

From system/library/cart/cart.php:345: 
/**
 * Update cart quantity
 *
 * @param int $cart_id
 * @param int $quantity
 */
public function update(int $cart_id, int $quantity): void {
    $this->db->query("
        UPDATE `" . DB_PREFIX . "cart` 
        SET `quantity` = '" . (int)$quantity . "' 
        WHERE `cart_id` = '" . (int)$cart_id . "'
            AND `customer_id` = '" . (int)$this->customer->getId() . "'
            AND `session_id` = '" . $this->db->escape($this->session->getId()) . "'
    ");
    
    $this->data = [];
}

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Removing Products

From system/library/cart/cart.php:377: 
/**
 * Remove product from cart
 *
 * @param int $cart_id
 */
public function remove(int $cart_id): void {
    $this->db->query("
        DELETE FROM `" . DB_PREFIX . "cart` 
        WHERE `cart_id` = '" . (int)$cart_id . "'
            AND `customer_id` = '" . (int)$this->customer->getId() . "'
            AND `session_id` = '" . $this->db->escape($this->session->getId()) . "'
    ");
    
    unset($this->data[$cart_id]);
}

​
Getting Products

From system/library/cart/cart.php:75: 
/**
 * Get all cart products
 *
 * @return array
 */
public function getProducts(): array {
    if (!$this->data) {
        $cart_query = $this->db->query("
            SELECT * FROM `" . DB_PREFIX . "cart` 
            WHERE `store_id` = '" . (int)$this->config->get('config_store_id') . "'
                AND `customer_id` = '" . (int)$this->customer->getId() . "'
                AND `session_id` = '" . $this->db->escape($this->session->getId()) . "'
        ");
        
        // Process cart items with product data, options, pricing, etc.
        // Returns enriched product data
    }
    
    return $this->data;
}

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Cart Calculations

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Get Subtotal

From system/library/cart/cart.php:449: 
/**
 * Get cart subtotal
 *
 * @return float
 */
public function getSubTotal(): float {
    $total = 0;
    
    foreach ($this->getProducts() as $product) {
        $total += $product['total'];
    }
    
    return $total;
}

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Get Total Weight

From system/library/cart/cart.php:428: 
/**
 * Get total cart weight
 *
 * @return float
 */
public function getWeight(): float {
    $weight = 0;
    
    foreach ($this->getProducts() as $product) {
        if ($product['shipping']) {
            $weight += $this->weight->convert(
                $product['weight'],
                $product['weight_class_id'],
                $this->config->get('config_weight_class_id')
            );
        }
    }
    
    return $weight;
}

​
Get Taxes

From system/library/cart/cart.php:468: 
/**
 * Get cart taxes
 *
 * @return array
 */
public function getTaxes(): array {
    $tax_data = [];
    
    foreach ($this->getProducts() as $product) {
        if ($product['tax_class_id']) {
            $tax_rates = $this->tax->getRates($product['price'], $product['tax_class_id']);
            
            foreach ($tax_rates as $tax_rate) {
                if (!isset($tax_data[$tax_rate['tax_rate_id']])) {
                    $tax_data[$tax_rate['tax_rate_id']] = $tax_rate['amount'] * $product['quantity'];
                } else {
                    $tax_data[$tax_rate['tax_rate_id']] += $tax_rate['amount'] * $product['quantity'];
                }
            }
        }
    }
    
    return $tax_data;
}

​
Usage Examples

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Add to Cart

// In controller
if (isset($this->request->post['product_id'])) {
    $product_id = (int)$this->request->post['product_id'];
    $quantity = isset($this->request->post['quantity']) ? (int)$this->request->post['quantity'] : 1;
    $option = isset($this->request->post['option']) ? $this->request->post['option'] : [];
    
    $this->cart->add($product_id, $quantity, $option);
}

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Display Cart Contents

$data['products'] = [];

foreach ($this->cart->getProducts() as $product) {
    $data['products'][] = [
        'cart_id'   => $product['cart_id'],
        'name'      => $product['name'],
        'model'     => $product['model'],
        'quantity'  => $product['quantity'],
        'price'     => $this->currency->format($product['price'], $this->session->data['currency']),
        'total'     => $this->currency->format($product['total'], $this->session->data['currency']),
        'remove'    => $this->url->link('checkout/cart.remove', 'cart_id=' . $product['cart_id'])
    ];
}

$data['totals'] = [
    'subtotal' => $this->currency->format($this->cart->getSubTotal(), $this->session->data['currency']),
    'total'    => $this->currency->format($this->cart->getTotal(), $this->session->data['currency'])
];

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Next Steps

Database Library

Database operations

Session Library

Session management